In general, a circuit breaker operates to engage and disengage a selected electrical circuit from an electrical power supply. The circuit breaker ensures current interruption thereby providing protection to the electrical circuit from continuous over current conditions and high current transients due to, for example, electrical short circuits. Such circuit breakers operate by separating a pair of internal electrical contacts contained within a housing (e.g., molded case) of the circuit breaker. Typically, one electrical contact is stationary while the other is movable (e.g., typically mounted on a pivotable contact arm).
The contact separation may occur manually, such as when a person throws an operating handle of the circuit breaker. This may engage an operating mechanism, which may be coupled to the contact arm and moveable electrical contact. Otherwise, the electrical contacts may be separated automatically when an over current, short circuit, or fault condition is encountered. Automatic tripping may be accomplished by an operating mechanism actuated via a thermal overload element (e.g., a bimetal element) or by a magnetic element, or even by an actuator (e.g., a solenoid).
Upon separation of the electrical contacts by tripping, an intense electrical arc may be formed in than arc chamber containing the electrical contacts. This separation may occur due to heat and/or high current through the circuit breaker or due to sensing a ground or other arc fault. It is desirable to extinguish the arc as quickly as possible to avoid damaging internal components of the circuit breaker.
In low voltage alternating current (AC) circuit breakers, such as molded case circuit breakers (MCCBs), two methods are commonly used to extinguish arcs. The first method is often referred to as current limiting and it includes actively raising the arc voltage to a level higher than the system voltage, which effectively forces the current to reduce to zero. Commonly used current limiting methods include providing arc plates, outgassing material, and designing long arcs. The second method includes using the natural current zero crossing from AC circuit to prevent re-ignition after current goes to zero.
In some currently-available circuit breakers, due the inductance present in a circuit, a recovery voltage can be induced across the arc chamber. If the recovery voltage in the arc chamber is high enough, this can re-ignite the extinguished arc and cause failed or delayed interruptions and additional wear of the contacts and surrounding components.
Accordingly, there is a need for apparatus and methods to rapidly extinguish an electrical arc in a circuit breaker resulting from contact separation.